Liquid crystal displays (LCDs) are widely used in screen displays. According to initial alignment of liquid crystal, electrode structure and physical properties of liquid crystal, liquid crystal displays may be divided into modes as follows: Twisted Nematic (TN), Vertical Alignment (VA), In-plane Switching (IPS), Fringe Field Switching (FFS), ADvanced Super Dimension Switch (ADS), and so on.
An LCD has shortcomings of small-range and anisotropy of viewing angles, that is, its contrast decreases significantly when viewed along a direction deviated from a vertical line of the display panel. As to the current developing trend of LCD of large size and the situation of several people viewing, such shortcomings become particularly noticeable. Thus, in order to improve characteristics of viewing angles of an LCD, various techniques for achieving wide-viewing angles are proposed, such as IPS, FFS, ADS, MVA (Multi-domain vertical alignment), etc., all of which can increase the viewing angles of a liquid crystal display.
For example, for a liquid crystal display without an optical-compensation film, when viewed along a direction at a vertical viewing angle, as illustrated in FIG. 1, the projection axis of a lower polarizing sheet, the absorption axis of an upper polarizing sheet, as well as the optical axis of liquid crystal, are all at point A as indicated in the figure, and therefore this will not cause dark-state light leakage.
However, when viewed along an oblique direction, the projection axis of the lower polarizing sheet, the absorption axis of the upper polarizing sheet, as well as the optical axis of the liquid crystal, all deflect. For example, in a case where a polar angle is 60° and an azimuth angle is 45°, as illustrated in FIG. 2, the projection axis of the lower polarizing sheet is at the position of point T, whereas the absorption axis of the upper polarizing sheet as well as the optical axis of the liquid crystal are both at the position of point A, so the light entering from the lower polarizing sheet is at the point T, and after the action of the liquid crystal, arrives at point B as indicated by the arrow direction, resulting in that the light can not be completely absorbed by the absorption axis of the upper polarizing sheet, thereby causing light leakage. This results in poor contrast in an oblique plane, and therefore seriously affects the display quality of the LCD.